Herd health

Herd Healthby Nigel Edwards MVB MRCVS

The Irish Moiled Cattle Society actively promotes and encourages its members/breeders to have a high health status within all Irish Moiled herds. This can be achieved if all cattle breeders belong to a Cattle Health Certification Standards (CHeCS) scheme. This scheme is of an accredited standard for the monitoring, control and ultimately eradication of four diseases; BVD, Johne’s disease, IBR and Leptospirosis.

The CHeCS scheme is joined on a voluntary basis and herd owners may test for any or all of the diseases. Where to start depends on a herd’s individual circumstance. The entry level into a cattle health schemeroutine monitoring, which can be done conveniently from the samples of blood taken at the annual TB/brucellosis test. This will give a good assessment of the health status of the herd. Once the health status is known, a herd may progress through a programme of control and eradication to eventual accreditation of disease free status.

The main two diseases for which tests should be taken are BVD and Johne’s disease. These are the two most problematic diseases. If a herd owner bought in an animal that was a carrier for either of these diseases the consequences could be drastic.

Therefore, herd owners should only buy stock from other herd owners who are members of the herd health scheme. Similarly, sellers of breeding stock should be members of the herd health scheme in order to guarantee that they are sellingfree stock.

To find out more, and to get your own herdon the herd health scheme then contact yourVeterinary Practitioner.

A little about these two diseases:

Johne’s Disease;This is a disease of cattle that causes chronic, progressive, wasting due to diarrhoea. The infectious agent is shed in large numbers in faeces and is also found in colostrum. Animals are infected by ingesting the agent and young animals (especially in the first month of life) are considered to be the most susceptible to infection. Therefore, a calf out of an infected mother will always become infected. Even though cattle are infected at a young age, clinical signs of diarrhoea and weight loss usually do not occur until the animal reaches approximately 3-5 years of age, or even older.

Infection is nearly always introduced to the herd by purchasing infected replacement breeding stock, including bulls.

A test carried out on a blood sample to detect antibodiesimmune response)valuable for the diagnosis of Johne’s disease. However, this test can only detect infected animals in the later stages of the disease, when clinicalhave become apparent, or in the short periodto this. This means that infected animals may test negative on several occasionsannual tests before they test positive. Testing individual animals at the point of sale is therefore of very limited value.However, the test is very useful as an indicatorthe herd infection. If all animals in arepeatedly test negative for theat annual intervals, thenherd can be categorised as free from Johne’s Disease. Ideally, breeding stock should be bought from these herds.If an animal does show positive in a blood test, that animal and also any offspring of a positive female should be removed from the herd. In this case, a further three clear annual tests of all animals in the herd have to occur in order for that herd to be categorised as free from Johne’s Disease.

BVDBovine viral diarrhoea (BVD) virus causes a complex of diseases in cattle. BVD virus can cause diarrhoea, which is usually mild but is occasionally severe, even in adult cattle.virus infection is also believed to cause significant suppression ofimmune systemmay contribute to the pneumonia and scour complex in calves. Infection immediately before or during the breeding season will reduce conception rates and causes early death of the embryo.

The virus can also cause deformities in the calf. However, of particular importance is infection in the first third of pregnancy. When developing calves survive, they remain persistently infected (PI) with the virus. It is these PI calves that, once born, provide the major route of spread for the virus. They often appear normal, but they shed the virus throughout their lives. Many develop a fatalof diarrhoeaas Mucosal Disease before they reach maturity (approximately 18 months of age). However, significant numbers of PI cattle survive well into adulthood. All offspring of a PI dam or a PI sire will also be a PI.

All breeding stock bought, in particular young bulls should be tested for BVD virus, if they are not bought from a herdwho is a membera herd health scheme.

The economic losses from an uncontrolled outbreak of BVD can be very high, and indeed the nation of Northern Irelandthe present time isto put ain place to eradicate this diseasea national level. will only ever be achieved if herd owners voluntarily get involved and help to try and eradicate this disease. Scotland, Republic of Ireland and other countries across mainland Europe already have a programme in place to eradicate BVD nationally.

A blood sample from an individual animal can be usedfor the BVD virus. Once an animal has been deemed clear of BVD virus, it will always be clear. So, for a herd, in the first year all animals are screened, in the second year and subsequent years only the calf cropscreening. A dozen calf blood samples can be pooled together and a test for the genetic material of the virus (PCR test) can be employed to minimise cost. If a PI animal is identified in a herd then removal of that animal is essential. Along withfor PI animals a high level of bio-security is required to exclude sources of re-infection or a vaccination programme of breeding stock should be in place.